Startup Speaker Build (help)

[eyekyu]

I just recently bought an Onkyo 607. HUGE UPGRADE from my old JVC receiver.
Now, Looking to upgrade my speakers and adding a center and sub.

Im looking at Polk Audio 50s for fronts, $99/speaker seems like a killer deal. Bookshelf or Floor Standing don't matter and doesnt have to be Polk.

Center, Im not sure what to look for in getting one of these.

Sub, just having a hard time weather I should get a 8" or 10" if the difference in price worth it? good brand.

Surround/Rear speakers ill wait till i get my house.

any kind of help is greatly appreciated